1. Field of the Invention
The present invention relates to a variable and steady yarn feeding device, and more particularly to a yarn feeding device of a circular knitting machine having a variable and a steady yarn feeding features.
2. Description of Related Art
Fabric, knitted by a circular knitting machine, has a variety of styles recently. It is required to add a variable yarn feed to a steady yarn feed in order to knit a variety of fabrics by configuring the yarn into a number of different tension yarns during the knitting process. As such, a yarn feeding apparatus having a variable yarn feed and a steady yarn feed features is desirable.
For example, a U.S. Pat. No. 4,890,464 entitled "POSITIVE FEEDING DEVICE FOR CIRCULAR KNITTING MACHINE" is provided to accomplish such goal. The apparatus comprises a yarn feeding mechanism, driven by a drive means, having a first yarn guide surface and a second yarn guide surface. A yarn lead-in side of the first yarn guide surface has a first yarn guide device provided, and a yarn lead-in side of the second yarn guide surface has a second yarn guide device provided respectively.
The U.S. Pat. No. 4,890,464 is characterized in that the friction between the yarn and the first yarn guide surface is larger than that between the yarn and the second yarn guide surface. As such, the yarn is fed through the second yarn guide surface for a plain knitting when the yarn feed is steady, while the yarn is fed through the first yarn guide surface for a jacquard knitting when the yarn feed is variable. As a result, a yarn feeding apparatus having a variable yarn feed and a steady yarn feed features is provided.
However, the prior art is unsatisfactory for the following reason. As to the first yarn guide surface, the yarn feed or not is determined by the friction between the yarn and the resilient surface as well as the tension of the yarn demand. As such, a maximum contact area between the yarn and the resilient surface is desirable for fulfilling the purpose of a large demand. In contrast, a minimum contact area (or even no contract) between the yarn and the resilient surface is desirable when there is no demand for avoiding yarn feed. It is noted the contacting angle or area between the yarn and the resilient surface is adjustable only by rotating the position of the first yarn guide device. It is claimed that the contacting angle or area between the yarn and the resilient surface is adjustable by changing the position of the first yarn guide device through a manual operation.
However, in fact, it is impossible for an operator to instantly and accurately adjust the position of the first yarn guide device during the knitting process if there is a sudden change of yarn demand. Accordingly, in practice, the first yarn guide device is pre-set to an intermediate position, i.e., an angle between the yarn and the resilient surface is between the maximum yarn feed (i.e., a maximum contacting angle between the yarn and the resilient surface) and no feeding (i.e., no contact or a minimum contacting angle). As such, a high rate of fabric fault is occurred if the first yarn guide device is not adjusted to an optimum position and/or the quality of the yarn is poor in detail, it is possible for the feeding quantity of yarn being not sufficient to the demand due to a small friction between the yarn and the resilient surface. Further, it is possible for a continuous yarn feed even if there is no demand due to a high friction between the yarn and the resilient surface. As a result, a poor fabric such as irregularity will be knitted.
An another prior art, a preferred embodiment of variable feeding device, is disclosed in U.S. Pat. No. 3,606,975 entitled "METHOD OF FEEDING YARN TO A KNITTING PLACE ON A TEXTLE MACHINE". The patent discloses the yarn feed speed is controlled by a detection circuit of the tension ring. Generally, the precision of an electronically controlled device is very high. However, the speed control of the motor is sometimes interfered by the environment when the yarn consumption is intermittent. Further, the knitting machine owner is mostly bothered by the unacceptable high fault rate of the tension ring which being in contact with the yarn frequently. Furthermore, it is required to replace the tension ring whenever there is a change in the yarn feed. As such, a frequent change of the tension ring and/or the tension ring adjustment is inevitable for knitting a variety of fabrics. This is a time-consuming process as well as a possible damage to the tension ring caused by such replacement. These drawbacks have not been solved in a kniting machine of the patent disclosed.
Thus, it is desirable to provide a variable and steady yarn feeding apparatus in order to overcome the above drawbacks of prior art.